The important roles of the basement membranes include: (a) organization of tissue during embryonic development, (b) attachment of cells layers to their associated connective tissue elements, and (c) filtration of molecules according to size and net charge. Alterations in the morphology of basement membranes have been observed in various diseases such as glomerulonephritis, diabetes mellitus, immune renal disease and congenital nephrosis. Yet, biochemical characterization of the glycoproteins comprising these structures has been slowed by the insoluble nature of basement membrane collagen. In fact, thus far sequence analysis has not been reported for any basement membrane collagen (type IV collagen). We have purified a soluble basement membrane glycoprotein from urine individually pooled from a group of normal individuals. Amino acid analysis, carbohydrate determination, and sequence analysis have confirmed that this protein is one of many fragments of basement membrane glycoproteins present in normal urine. The presence of hydroxyproline, hydroxylysine and the presence of glycine in every third position are typical of collagen. The finding of 24 residues of glucosamine and 4 residues of galactosamine is typical of basement membrane collagen. The soluble nature of basement membrane collagen fragments excreted in normal urine eliminates the necessity to solubilize by reduction in the presence of SDS or urea or to digest with proteolytic enzymes, procedures necessary for separation of collagen glycoproteins from surrounding tissue. Sequence analysis and carbohydrate determination of these will permit for the first time the characterization of large portions of human basement membranes: (a) in different age groups of normal individuals, (b) in individuals with early and late onset diabetes mellitus and (c) in individuals with inherited defects of the tubular and glomerular membranes. Sequence analysis of basement membrane glycoproteins will permit the comparison of interstitial collagen (Types I, II, and III) to basement membrane collagen in order to determine the c genetic relationship of these types.